Among personal computers as information processing apparatus, recently, so-called notebook-sized personal computers are widely used. Notebook-sized personal computers are small and portable, and occupy a small space on a desk, and various professional types are manufactured.
FIG. 5 is a perspective view of a conventional notebook-sized personal computer having a display panel serving also as an input tablet, and allowing both keyboard input and tablet input. FIG. 6A and FIG. 6B are side views showing two closed states of a display unit in the conventional notebook-sized personal computer. FIG. 7 is a perspective view for explaining a method of use of a tablet of the conventional notebook-sized personal computer.
In FIG. 5, this notebook-sized personal computer comprises a main body 101 and a display unit 102, which are coupled through a hinge 105. The display unit 102 has a display panel 103 and a button 121, and the display panel 103 is protected by a back cover 104. The display panel 103 is also a tablet for pen input. The hinge 105 has axes of rotation in two mutually orthogonal directions. A first axis of rotation is an opening and closing axis of the main body 101 and display unit 102. This opening and closing direction is indicated by arrow 105a. The display unit 102 is thus opened and closed, and has a free end 102a and a fixed end 102b. A second axis of rotation is a rotating axis defining a rotating direction of the display unit 102. This rotating direction is indicated by arrow 105b. 
FIG. 6A is a side view of a personal computer in a finished state after closing the display unit 102 from the state in FIG. 5. FIG. 6B is a side view of a personal computer in a closed state of the display unit 102 after rotating the display unit 102 in FIG. 5 by 180° in the direction of arrow 105b. A carrying strap 108 is attached to the main body 101. In FIG. 6A and FIG. 6B, the same reference numerals as in FIG. 5 refer to the same parts as in FIG. 5, and their explanation is omitted.
When a personal computer is used in an office, usually, the personal computer is put on a desk, and the keyboard 106 is operated by both hands as shown in FIG. 5. After work, as shown in FIG. 6A, the display panel 103 is folded inside, and it is portable in this state.
When a personal computer is used outdoors, the display panel 103 is opened upward as shown in FIG. 6B and a pen input device 107 is manipulated. FIG. 7 is a perspective view showing a holding method of the personal computer in the case of pen input in outdoor use. The personal computer is held by one hand by passing fingertips through the strap 108, and the pen input device 107 detached from the main body 101 is held by the other hand, and pen input is made in a specified region of the display panel 103 functioning as a tablet. In FIG. 7, the same reference numerals as in FIG. 5 refer to the same parts as in FIG. 5, and their explanation is omitted.
In the personal computer having such structure, in this state, the display shown in the display panel 103 is inverted upside down between the keyboard input as shown in FIG. 5 and the pen input as shown in FIG. 7. Accordingly, the display direction must be changed over. That is, in FIG. 5, the upper side of the screen must be located near the free end 102a. And in FIG. 7, the lower side (front side) of the screen must be near the free end 102a. The button 121 is provided for rotating the display panel by 180°, and by manipulating this button 121, the display direction of the display panel 103 can be changed over manually.
Although it is not of the pen input type, Japanese Laid-open Patent No. H8-179851 discloses an apparatus having an exposed protrusion and a switch for changing over the display direction of the screen automatically.
Common problems of the portable personal computers are portability and power saving. In addition, portable personal computers for professional use are required to have a higher toughness than the personal computers used indoors. The personal computer shown in FIG. 5 is also used for professional purposes. Therefore, during use as shown in FIG. 7, it is required to have shock durability to withstand dropping of the personal computer main body by mistake or hitting against any hard object, shaking durability to withstand shaking during carrying, and resistance to rain and water drops, dust and others during outdoor use.
Therefore, as in the prior art, if the button, protrusion or switch for changing over the display direction is provided on the outer side, the shock durability, or protection from water drops or dust cannot be satisfied.